1. Field of the Invention
The present invention relates in general to heat exchanger assembly fixtures for securing assembly components thereto and passing through a brazing furnace to join the assembly components into a singular unit to provide a heat exchanger for use in motor vehicle air conditioning systems.
2. Description of the Prior Art
Prior art brazing fixtures have been used for passing heat exchanger assembly components through a brazing furnace to join the components into a singular unit, which comprises a heat exchanger for use in a motor vehicle air conditioning system. The heat exchanger components are often made of an aluminum alloy having a brazing clad. Typically, the heat exchanger components are secured to a brazing fixture to hold the components in proper alignment for passing through a brazing furnace, flowing the brazing clad and fusing the components together. If the brazing fixture does not hold each of the components in the proper alignment, the heat exchanger may be formed with unacceptable defects.
Such unacceptable defects include the phenomena which occurs when fin stock within heat exchangers does not stay within acceptable tolerances for alignment with heat exchanger refrigerant flow tubes. This category of defect is often termed "high fin". Fin stock is flexible, and requires mechanical support to extend for any significant length in a particular direction. This is usually not a problem when heat exchanger assemblies are passed through brazing furnaces in a vertical disposition. However, when heat exchanger assemblies are passed through brazing furnaces in a horizontal disposition, that is, laid on their sides, mechanical support is essential to retain the fin stock in a properly aligned position.
Mechanical support for fin stock has been supplied by forming and assembling refrigerant flow tubes in heat exchanger assemblies with clearances between the flow tubes sized for retaining the fin stock in position. Further, prior art brazing fixtures have been supplied with bars and bands for retaining the fin stock in position. However, the bars and bands of prior art brazing fixtures extend only partially over the length of pieces of fin stock, usually retaining the fin stock at only two places along the length of a particular piece of fin stock. Prior art brazing fixtures only fully extended along the ends of a heat exchanger assembly, not the side faces through which cooling air is intended to pass during in actual operation of the finished heat exchanger.
FIG. 1 is a cross sectional view of a heat exchanger 11 secured to a prior art brazing fixture 12, and depicts the phenomena termed "high fin." Heat exchanger 11 is formed by a plurality of components which include header tanks 13, refrigerant flow tubes 15, and fin stock 17. The plurality of heat exchanger components 13, 15, and 17 are secured to prior art brazing fixture 12 by two metal bands 19. The two bands 19 do not extend all the way across the length of flow tubes 15 and fin stock 17, rather they only secure fin stock 17 within refrigerant flow tubes 15 at two places. Thus, portion 25 of fin stock 17 is free to sag with a high fin displacement such that fin stock edge 21 extends beyond edge 23 of refrigerant flow tubes 15.
If the high fin displacement at portion 25 of fin stock 17 exceeds acceptable quality control parameters, the heat exchanger is rejected and must be either scrapped or reworked until the high fin displacement in portion 25 falls within acceptable parameters. Thus, high fin results in lower production yield rates and additional rework steps, increasing costs for producing heat exchangers.